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Structure and
replication :
Human papillomaviruses (HPV) measure 50 nm in diameter. Classification of HPV is based on DNA sequence homology, more than 70 HPV types have been identified.
Pathogenesis :
Papillomaviruses infect and replicate in cutaneous and mucosal epithelium, including epithelial proliferations. Viral infection remains local and generally regresses spontaneously. Viral DNA has been found in both benign and malignant tumours.
Epidemiology :
Skin warts, plantar warts, common warts and flat warts are most common in childern and young adults. Genital condylomas are most common among sexually active patients. Laryngeal papillomas are found most commonly in young childern. HPV infections are transmitted by direct contact. Virus can be found on bathroom floors and towels. Inoculation during sexual intercourse or while passing through an infected birth canal, or by the childhood habits of chewing warts is known to occur.
Clinical
Syndromes :
1. Skin warts : Most persons are infected with the common HPV types (1-->4), which infect keratinized surfaces usually on the hands and feet and occur frequently in childhood or early adolescence. 2. Laryngeal warts : Laryngeal papillomas are commonly associated with HPV6 and HPV-11. Multiple laryngeal warts (laryngeal papillomatosis) is usually considered a life-threatening condition in childern because of the danger of airway obstruction. 3. Anogenital warts : Genital warts (condyloma accuminata) occur almost exclusively on the squamous epithelium of the external genitalia and perianal areas and about 90% are also caused by HPV types 6 and 11. 4. Cervical cancer : Neoplastic HPV infection of the genital tract is now recognized as a common sexually transmitted disease. It can envolve in patient with genital warts through grades of cervical dysplasia to invasive cancer. Infection of the female genital tract by HPV types 16 and 18 and, rarely by other types e.g. 31, 33, 35 & 39 is associated with intraepithelial cervical neoplasia and cancer. The same serotypes are also associated with penile and vulvar cancers as well as laryngeal and oesophageal carcinomas. Coinfection with herpes simplex virus and tobacco smoke are suspected co-factors involved in the progression of high-risk HPV lesions to cancer.
Laboratory
Diagnosis :
Molecular probes are the method of choice of establishing the presence of HPV genomes in cervical swabs and in tissue. Human papillomaviruses don't grow in cell cultures, and tests for HPV antibodies are rarely used exept in research surveys.
Treatment,
Prevention and Control :
Spontaneous disappearance of warts is the rule, but this may take many months to years so intervention is sometimes warranted, especially for painful or bulky lesions. Removal by surgical cryotherapy, electrocautery or chemical means can be effective, although recurrences are common. The best means of prevention is avoidance of direct contact with infected tissue. |
Human Papillomaviruses
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